The present invention relates to a method of producing an open pollinated hybrid and to open pollinated hybrids of corn and sunflowers.
The publications and other materials used herein to illuminate the background of the invention or provide additional details respecting the practice, are incorporated by reference, and for convenience are respectively grouped in the appended List of References.
Domestic (cultivated) corn is primarily a creation of prehistoric Native North American breeders. Selection was carried out on corn producing a vast array of varieties and types of corn. Maturities ranged from 60 days to maturity to 160 days to maturity. Grain hardness ranged from soft floury to hard flinty. Grain color ranged from deep purple to pale white with all the shades in between. Since corn is a cross pollinated plant type, the Native American breeders made selections of material plant types with no control of the pollen (male) parent. This type of selection is called half sib selection. Thus, corn was developed as an open pollinated crop, spread across North America, with numerous local varieties adapted to local conditions. All of the commercially grown corn, world wide, is derived from this North American germplasm pool.
The European colonists that came to the New World (North America) used the Native American open-pollinated varieties as they found them and continued the method of half sib selection to improve yield and agronomic qualities. This method of breeding continued into the 20th Century with the local varieties across North America representing separate gene pools based on the original Native American open pollinated varieties. The type of grain preferred by colonial breeders was a medium textured seed of yellow color with a flinty outer endosperm enclosing an inner soft floury endosperm. As drydown progresses the soft endosperm collapses and an indentation is formed on the crown of the corn kernel, thus the name xe2x80x9cyellow dentxe2x80x9d was applied to this type of corn grain. Yellow dent corn is the predominant version of the grain that is used worldwide for food, feed and fuel.
At the beginning of the 20th Century, genetic researchers began to self-pollinate corn. Selfing used bags over the ears and the silks to control the flow of pollen from the tassel to the silks of individual plants. Successive generations of self pollinating (selfing) resulted in a continuing loss of vigor with plants becoming weaker and less able to produce seed in quantity. To those skilled in the art this phenomena is known as xe2x80x9cinbreeding depressionxe2x80x9d. It is also well known to those skilled in the art that when weak unrelated inbreds were crossed, the resultant progeny (seed) gave rise to plants that were many times more vigorous and higher yielding than the parents. This phenomena is known as xe2x80x9chybrid vigorxe2x80x9d; the progeny seed is known as hybrid (F1) seed.
While it was possible to produce hybrid vigor with reference to weak inbred lines, it was not initially apparent when inbreds were derived from one of the accepted commercial open pollinated varieties and the standard for yield and vigor was such a commercial variety. However after much trial and error research it was discovered that when inbreds were selected from a range of the adapted open pollinated varieties from widely divergent geographic areas that hybrids were produced that yielded far more than the open pollinated varietal parents with a far more uniform population of plants. It became clear that certain varieties when crossed together yielded commercial grade hybrid vigor, but most did not. The special populations (open pollinated varieties) that produced hybrid vigor when combined were called heterotic groups. The major heterotic groups are listed in Table 1:
As an example, it was found that when inbreds derived from Reid Yellow Dent were crossed with inbreds from Lancaster Surecrop produced hybrids that far out-yielded any commercial open pollinated variety. From this process/product the hybrid seed corn industry began. The first hybrids became available in the 1930s and by the late 1950s virtually all of the open pollinated corn varieties had been replaced by hybrids.
The actual mechanism of hybrid vigor is still poorly understood, with the result that genetic improvement has been confined to breeding and selection within the heterotic groups. Thus one can improve the stalk strength and yield of C103 but the basic genetic background of C103 must be maintained so that the hybrid relationship with Stiff Stalk Synthetic (SSS) is maintained. This results in a cumbersome breeding process in which improved lines must always be evaluated in reference to specific heterotic mates. For example an improved line from C103 can be produced but if it fails to yield hybrid vigor with SSS it is discarded. Therefore, hybrid breeding is an expensive process.
The actual production of hybrid seed is also an expensive process. In a production field two inbred parents are planted. One is a female plant upon which the hybrid seed will be produced. This plant must be detasselled prior to pollination or genetically male sterilized. The second plant is a male pollen parent used to pollinate the female plant. The seed of this male plant is not harvested for hybrid seed. Thus to produce hybrid seed it is necessary to use weak yielding inbreds as seed producing parents, and to use non-seed producing parents as pollinators. Based on a variety of environmental conditions, the male and female plants may fall out of synchronization with silking and pollination timing resulting in reduced or non-existent seed production. For all the above reasons, hybrid seed production is expensive and somewhat complicated, with the result that hybrid seed production and the resultant hybrid seed is unavailable to many subsistence farmers in developing countries that need it most.
Like corn, sunflower is a crop that was developed by the Native Americans before the arrival of the European explorers and settlers. It was used as a nutritious oily food crop often complementing corn in their diets. It had an additional dimension in that certain selected varieties produced purple, colorant bearing hulls with high levels of anthocyanin pigment. These hulls were used in a boiling water type treatment to color the clothes and blankets of the people. Colors ranged from red to blue depending on the treatment of the hull material (anthocyanins are color sensitive to pH values with low pH levels yielding red colors and higher pH levels yielding blues). The sunflower seed of commerce is an achene, which is a dry fruit with the hard woody hull representing ovary tissue with the kernel representing the ovule (seed). The Native Americans would consume the sunflower as whole achenes (often roasted) or as shelled kernels. The hulls of the sunflower can be any color with black, white, black/white striped and purple being most common. The sunflower traveled from the New World and found its way to Europe where it found special acceptance as a cool climate oil seed crop in Russia. In the first half of the 20th Century under V.S. Pustovoit, a number of widely adapted open pollinated (OP) black hulled oil seed varieties (not hybrids) with oil content greater then 40% were developed. The old Native American land varieties had oil content of about 30%. As with corn, all breeding work on sunflower prior to the development of hybrids was accomplished with half sib selection techniques both in the New World and Russia. Russian OP varieties were introduced into the Northern Great Plains (Minn, N.Dak., S.Dak.) in the 1960s. The OP variety Peredovik was especially successful and widely grown. However, the disuniformity of this OP variety and the lack of stalk strength made the American farmers desire an improved varietal type and hopefully a hybrid type. This was a difficult task because the sunflower is not easily male sterilized as is corn in which tassels are removed. In corn, the male (tassels) and female (silk) organs are at separate positions on the plant. In sunflower, the male and female sex organs are collocated in tiny individual florets (1000 to 3000 per sunflower head). Thus making a sunflower hybrid was a commercial impossibility.
However, in 1969, Dr. Leclerq of France, through interspecific crosses developed a stable and usable cytoplasmic male sterile system (CMS) for sunflower that yielded sunflower plants and thus lines that produced plants that were 100% male sterile. Such plants could serve as females in the production of sunflower hybrids. These types of plants are called A lines and must be maintained (pollinated) by pollen producing equivalent lines called B lines. Thus, each female A line must have an equivalent (identical in appearance) B line (as a pollen donor) in order to maintain the A line (produce seed) since no pollen is produced by the A line. An A line is created by backcrossing the CMS trait into a selected B line parent. In 1970, just one year after Leclerq""s discovery of the CMS trait, Dr. Kinman (USDA) and others discovered nuclear genes for fertility restoration in wild sunflower and soon restoration genes were transferred (backcrossed) into branched oil seed and confectionary parental (male) lines called R (restorer lines). These two discoveries made sunflower hybrids a reality by the early 1970s by a process in which a cytoplasmic male sterile (CMS) A line is crossed to a pollen producing restorer (R) line to yield a fully fertile F1 hybrid.
It is an object of the present invention to provide a method for producing high yielding corn and sunflower hybrids without having to produce a new crop of F1 hybrid seed for each growing season. The present invention provides a method to produce open pollinated corn and sunflower hybrids that can be increased by simple isolation techniques therefor eliminating the costly expense of continuous F1 hybrid seed production. The method of the present invention includes crossing inbreds from complementary heterotic groups to yield an F1, hybrid. This F1 hybrid is then selfed for 1 to 5 or more additional generations resulting in the following: F2 (second generation), F3 (third generation), F4 (fourth generation) and F5 (fifth generation) seed. A representative plant and/or plants and/or ear row(s) from the F2, F3, F4 or F5 generations are selected that retain the F1 hybrid characteristics for yield, agronomic qualities and general appearance. These selected F2, F3, F4 and F5""s are grown out in isolation as open pollinated hybrid seed. As long as isolation is maintained, the open pollinated hybrid can be increased in this manner with no loss of hybrid vigor.
In order to provide a better understanding of the specifications and claims contained in this application, definitions of some terms used therein are provided below:
Backcrossxe2x80x94As used herein, the term xe2x80x9cbackcrossxe2x80x9d means a cross of a hybrid to either of its parents.
Backcross Breedingxe2x80x94As used herein, the term xe2x80x9cbackcross breedingxe2x80x9d means a system of breeding whereby recurrent (repeated) backcrosses are made to one of the parents of a hybrid accompanied by selection for a specific character or characters.
Complementary Heterotic Inbred Linesxe2x80x94As used herein, the term xe2x80x9ccomplementary heterotic inbred linesxe2x80x9d means inbred lines, that when crossed, give rise to F1 hybrid s that display heterosis.
Cross pollinationxe2x80x94As used herein, the term xe2x80x9ccross pollinationxe2x80x9d means a cross between two different plants.
Field Isolationxe2x80x94As used herein, the term xe2x80x9cfield isolationxe2x80x9d means the separation of one group from another so that mating between or among groups is reduced to a frequency of less than 10%.
E1xe2x80x94As used herein, the term xe2x80x9cF1 xe2x80x9d means the first generation of a cross.
E2xe2x80x94As used herein, the term xe2x80x9cF2xe2x80x9d means a progeny obtained by self-fertilization of F1 individuals. If selfing is continued the F- level is iterated to reflect the number of selfed generation. Thus, it can proceed from F2 to F3 to F4 to F5, etc. until selfing has ceased.
Heterosisxe2x80x94As used herein, the term xe2x80x9cheterosisxe2x80x9d means hybrid vigor such that an F1 hybrid falls outside the mean or range of the parents with respect to some character or characters. Usually applied to size, rate of growth, general thriftiness and seed yield.
Hybridxe2x80x94As used herein, the term xe2x80x9chybridxe2x80x9d means the product of a cross between genetically unlike parents.
Hybrid visorxe2x80x94As used herein, the term xe2x80x9chybrid vigorxe2x80x9d means the yield performance of an F1 hybrid exceeds the yield range of the parents.
Heterozygousxe2x80x94As used herein, the term xe2x80x9cheterozygousxe2x80x9d means having unlike (different) alleles at one or more corresponding loci (opposite of homozygous).
Homozygousxe2x80x94As used herein, the term xe2x80x9chomozygousxe2x80x9d means having like (the same) alleles at corresponding loci on homologous chromosomes. An organism can be homozygous at one, some, or all loci.
Inbred Linexe2x80x94As used herein, the term xe2x80x9cinbred linexe2x80x9d means a line produced by inbreeding. As used herein, an inbred line is considered to be any material that has undergone at least one self fertilization and includes F2, F3, F4, F5, F6 and all additional selfing generations.
Initial F1 Hybrid . As used herein, the term xe2x80x9cinitial F1 hybrid xe2x80x9d means the cross between two or more inbred lines.
Isolationxe2x80x94As used herein, the term xe2x80x9cisolationxe2x80x9d means a separation of one group from another so that mating among or between groups is reduced to a frequency of less than 10%.
Open pollinationxe2x80x94As used herein, the term xe2x80x9copen pollinationxe2x80x9d means the natural (uncontrolled) pollination that occurs within a cross pollinated population or variety.
Selectionxe2x80x94As used herein, the term xe2x80x9cselectionxe2x80x9d means discrimination among individuals in the number of offspring contributing to the next generation.
Self Fertilization (self pollination)xe2x80x94As used herein, the term xe2x80x9cself fertilization (self pollination)xe2x80x9d means the fusion of male and female gametes from the same individual. In this application often denoted by the short hand term xe2x80x9cselfingxe2x80x9d.
Selfing Generation linexe2x80x94As used herein, the term xe2x80x9cselfing generation linexe2x80x9d means a line produced by inbreeding. A xe2x80x9cselfing generation linexe2x80x9d is any genetic material that has undergone at least one self-fertilization and includes an F2, F3, F4, F5, F6 and all additional selfing generations.
Varietyxe2x80x94As used herein, the term xe2x80x9cvarietyxe2x80x9d means a group of individuals within a species which are distinct in form or function from other similar arrays of individuals.
The method of the present invention involves, in one embodiment, the crossing of two or more inbred lines to produce initial F1 hybrid s. These initial F1, hybrids were selfed for a number of generations to produce new inbreds (or selfing generation lines) that were tested with elite tester lines (potential heterotic counterparts). Unexpectedly, some of the inbred lines (F3, F4 and F5) retained the hybrid vigor of the initial F1, hybrid. When such lines were allowed to open pollinate in isolation, as a population for seed increase, there was little or no loss of hybrid vigor. One preferred embodiment of the method of the present invention is as follows:
1. Heterotic complementary inbred lines are crossed which result in a high yielding F1, hybrid (initial F1 hybrid );
2. This initial F1, hybrid is selfed for 1 to 4 or more generations to produce inbred lines;
3. Selected inbred lines (also called selfing generation lines) are grown in plots, which may be adjacent to the initial F1, hybrid, and are evaluated for general appearance, agronomic quality, seed quality (appearance), general disease resistance, and yield relative to the F1, hybrid; and
4. Inbred lines that equal or exceed the performance of the initial F1, hybrid and have a similar general appearance are selected, advanced and increased in isolation as an open pollinated hybrid.
5. Seed is further increased by simply repeating step 4 as needed.
The selfing process needed to produce inbred lines for this invention can generally be achieved after about four generations but any number of selfing generations can be used. Since selfing is an expensive and time consuming procedure it is desirable to complete this phase of the process as quickly as possible. However inbred lines of the present invention can be selected after any number of selfing generations, and often it just isn""t necessary to go beyond the F5 generation to select these lines.
The method of the present invention involves a breeding technique in which the hybrid vigor trait is fixed in the selfed lines and maintained in isolated cross pollinating production fields. This method has never been described or accomplished prior to this application. The end product of this process, an open pollinated corn hybrid having excellent yield has never been described or previously accomplished.